Class Policy

A Policy object is responsible for determining whether code executing
in the Java runtime environment has permission to perform a
security-sensitive operation.

There is only one Policy object installed in the runtime at any
given time. A Policy object can be installed by calling the
setPolicy method. The installed Policy object can be
obtained by calling the getPolicy method.

If no Policy object has been installed in the runtime, a call to
getPolicy installs an instance of the default Policy
implementation (a default subclass implementation of this abstract class).
The default Policy implementation can be changed by setting the value
of the policy.provider security property to the fully qualified
name of the desired Policy subclass implementation.

Application code can directly subclass Policy to provide a custom
implementation. In addition, an instance of a Policy object can be
constructed by invoking one of the getInstance factory methods
with a standard type. The default policy type is "JavaPolicy".

Once a Policy instance has been installed (either by default, or by
calling setPolicy), the Java runtime invokes its
implies method when it needs to
determine whether executing code (encapsulated in a ProtectionDomain)
can perform SecurityManager-protected operations. How a Policy object
retrieves its policy data is up to the Policy implementation itself.
The policy data may be stored, for example, in a flat ASCII file,
in a serialized binary file of the Policy class, or in a database.

The refresh method causes the policy object to
refresh/reload its data. This operation is implementation-dependent.
For example, if the policy object stores its data in configuration files,
calling refresh will cause it to re-read the configuration
policy files. If a refresh operation is not supported, this method does
nothing. Note that refreshed policy may not have an effect on classes
in a particular ProtectionDomain. This is dependent on the Policy
provider's implementation of the implies
method and its PermissionCollection caching strategy.

Constructor Detail

Policy

Method Detail

getPolicy

Returns the installed Policy object. This value should not be cached,
as it may be changed by a call to setPolicy.
This method first calls
SecurityManager.checkPermission with a
SecurityPermission("getPolicy") permission
to ensure it's ok to get the Policy object.

getInstance

This method traverses the list of registered security providers,
starting with the most preferred Provider.
A new Policy object encapsulating the
PolicySpi implementation from the first
Provider that supports the specified type is returned.

getInstance

A new Policy object encapsulating the
PolicySpi implementation from the specified Provider
object is returned. Note that the specified Provider object
does not have to be registered in the provider list.

getPermissions

Return a PermissionCollection object containing the set of
permissions granted to the specified CodeSource.

Applications are discouraged from calling this method
since this operation may not be supported by all policy implementations.
Applications should solely rely on the implies method
to perform policy checks. If an application absolutely must call
a getPermissions method, it should call
getPermissions(ProtectionDomain).

The default implementation of this method returns
Policy.UNSUPPORTED_EMPTY_COLLECTION. This method can be
overridden if the policy implementation can return a set of
permissions granted to a CodeSource.

Parameters:

codesource - the CodeSource to which the returned
PermissionCollection has been granted.

Returns:

a set of permissions granted to the specified CodeSource.
If this operation is supported, the returned
set of permissions must be a new mutable instance
and it must support heterogeneous Permission types.
If this operation is not supported,
Policy.UNSUPPORTED_EMPTY_COLLECTION is returned.

getPermissions

Return a PermissionCollection object containing the set of
permissions granted to the specified ProtectionDomain.

Applications are discouraged from calling this method
since this operation may not be supported by all policy implementations.
Applications should rely on the implies method
to perform policy checks.

The default implementation of this method first retrieves
the permissions returned via getPermissions(CodeSource)
(the CodeSource is taken from the specified ProtectionDomain),
as well as the permissions located inside the specified ProtectionDomain.
All of these permissions are then combined and returned in a new
PermissionCollection object. If getPermissions(CodeSource)
returns Policy.UNSUPPORTED_EMPTY_COLLECTION, then this method
returns the permissions contained inside the specified ProtectionDomain
in a new PermissionCollection object.

This method can be overridden if the policy implementation
supports returning a set of permissions granted to a ProtectionDomain.

Parameters:

domain - the ProtectionDomain to which the returned
PermissionCollection has been granted.

Returns:

a set of permissions granted to the specified ProtectionDomain.
If this operation is supported, the returned
set of permissions must be a new mutable instance
and it must support heterogeneous Permission types.
If this operation is not supported,
Policy.UNSUPPORTED_EMPTY_COLLECTION is returned.